This patent application incorporates by reference subject matter contained in the U.S. patent application titled "Method and Apparatus for Estimating Vehicle Braking System Effectiveness," the latter application having application Ser. No. 07/986,797, filed Dec. 8, 1992, now U.S. Pat. No. 5,299,452, having common inventors and assignee, and being filed simultaneously herewith. The subject matter of the referenced patent application is incorporated for reference purposes and is not essential to support the claims or to adequately disclose the invention of the present patent application.
Various systems for determining the need for vehicle braking system maintenance have been used. A common, "bookkeeping" method maintains records of the time elapsed and the number of miles travelled by a vehicle since its braking system has last been serviced so that such service can be performed before braking effectiveness declines to a critical level or to a level that incurs additional problems and/or expenses.
The bookkeeping method offers advantages of being uncomplicated and inexpensive. The conditions under which a vehicle may be driven during periods of similar duration, however, often vary between extremes, for example, heavy versus light traffic, hilly versus flat terrain, high versus low temperature and wet versus dry weather; and such extremes have a substantial affect on the rate and type of brake debilitation experienced. Consequently, the bookkeeping method cannot be expected to be consistently accurate; and disadvantages attending it include, at best, extra physical examinations and prematurely scheduled service and, at worst, service that is scheduled too late.
Brake lining wear does not always proceed at a linear rate, but it does require some time for wear to occur. Certain other parts of the braking system can, however, go from a fully functional condition to a nonfunctional condition very rapidly due to breakage or leakage resulting from the fatigue or damage to critical parts. If a nonfunctional part causes only a portion of the braking system to be nonfunctional or partly so, a driver might not notice the resulting decrease in braking efficiency for some time. During this period, additional damage is invited; and the linings of brakes remaining functional are likely to wear more rapidly than when all brakes are working with the same effectiveness.
The effectiveness of brakes associated with one set of axially associated wheels and the effectiveness of brakes associated with other sets of axially associated wheels must be balanced for optimum braking performance and efficiency. The two most common balance problems are fluid system imbalance and unequal brake torque due to differences in brake lining friction between brakes and to other mechanical problems.
While bookkeeping methods for determining the need for vehicle braking system maintenance function with a certain degree of efficiency, they do not provide the advantages of the improved method and apparatus of the present invention as is hereinafter more fully described.